﻿<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <DataTemplate x:Key="TestTemplate">
        <Button x:Name="SomeButton"></Button>
    </DataTemplate>

    <Style TargetType="ComboBox">
        <Setter Property="Background" Value="Green"></Setter>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="ComboBox">
                    <StackPanel Orientation="Horizontal" VirtualizingStackPanel.IsVirtualizing="True">
                        <Button x:Name="SomeButton">World</Button>
                        <TextBlock x:Name="SomeText">World</TextBlock>
                        <ItemsControl ItemTemplate="{StaticResource TestTemplate}" Foreground="{Binding Path=Background, ElementName=SomeButton}"></ItemsControl>
                    </StackPanel>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>